Optical absorption of warped nanographenes tuned by five- and seven-membered carbon rings

Abstract

The introduction of multiple carbon rings is one of the common ways for graphene modification. Starting from warped C80H30 nanographene, which consists of a number of six- and seven-membered carbon rings (C6 and C7) centering at a five-membered carbon ring (C5), we explored the structure and property variations of its derivatives in which their C7 rings were gradually replaced with C6 rings. With reducing number of C7 rings, their curved boundary with the C6 rings becomes flat until a bowl-like structure is formed when all the C7 rings disappear. The optical absorption spectra vary accordingly. Both the α-bands and the maximum absorption bands in the visible region are related to the number and location of the C7 rings. Further analysis of the excited states of the C80H30 derivatives, as well as on the designed model systems, revealed that the C7 rings affect the electron excitations in two ways. In addition to their participation in electronic transitions, they control the composition of molecular orbitals that are involved in the excitations. The highest occupied molecular orbitals are mainly contributed by atoms on the C6 and C7 rings, while the lowest unoccupied molecular orbitals by atoms on the C5 and C6 rings. Our study sheds some light on how the multiple carbon rings affect the optical absorption of nanographenes and provides information for the preparation of nanographenes with tunable structural and optical properties.

Electronic Spectra of Graphene in Far- and Deep-Ultraviolet Region: Attenuated Total Reflection Spectroscopy and Quantum Chemical Calculation Study

“…In the role of composite constituents, they offer enhanced barrier properties and improved mechanical properties, that is, stiffness, strength, and surface hardness. The graphene nanoflakes are in between oligo-layered graphene sheet and higher carbon–carbon structures (i.e., graphite), , and their optical − and transitional − properties are of high interest of general physical chemistry for wider understanding of carbon structures. The morphology and physicochemical properties of graphene have been studied by spectroscopy, that is, UV–vis, infrared, Raman, , circular dichroism, and X-ray photoelectron spectroscopy, as well as theoretical calculations, focusing not only on electronic structure and closely related properties ,,,,,,,− but also on morphology ,,,, and interactions. ,, Electronic properties of graphene not only remain in the center of attention of physical chemistry but also are essential for advanced material chemistry. − For example, graphene properties are being studied in the context of development of novel sensors , and nanoelectronics .…”

Negatively Curved Warped Nanographene Self-Assembled on Metal Surfaces

“…19 Interesting properties and potential applications of this warped nanographene have been investigated in recent studies. [19][20][21][22][23] For instance, it presents reversible reduction and oxidation behavior via charged intermediates suggesting that odd-membered ring defects in graphene can trap charges. Furthermore, C 80 H 30 has optical and electronic properties that differ from other all-carbon families and could have potential applications for future optoelectronic devices.…”

“…The unique structure of the C 80 H 30 molecule, where the presence of multiple odd-membered rings leads to a nontrivial double-concave structure, enhances characteristic properties which arise mainly from its nonplanar structure compared to planar analogues of similar size . Interesting properties and potential applications of this warped nanographene have been investigated in recent studies. − For instance, it presents reversible reduction and oxidation behavior via charged intermediates, suggesting that odd-membered ring defects in graphene can trap charges. Furthermore, C 80 H 30 has optical and electronic properties that differ from other all-carbon families and could have potential applications for future optoelectronic devices.…”